This invention relates to hydrophilic polymeric materials, to hydrophilic polymers having improved properties, and to the use of such polymers in fluid-absorbent products.
Hydrophilic polymers find extensive use in many applications in the form of foams and films. Hydrophilic foams, for example, can be integral component of sanitary napkins, tampons, diapers, wound and surgical dressings, and other products useful in absorbing bodily fluids. The utility of foams in such applications derives from their high affinity for aqueous liquids.
Unfortunately, the strong interaction between water and many hydrophilic foams often leads to swelling and to a significant loss in mechanical strength. For example, U.S. Pat. Nos. 4,554,297 and 4,508,854, both in the name of the present inventor, Dabi, disclose polymers which are the reaction products of epoxy resins and amine-terminated poly(alkylene oxide). In U.S. Pat. No. 4,554,297, an absorbent foam comprising an epoxy resin and amine-terminated poly(alkylene oxide) oligomers is described. The amine-terminated oligomers in that patent are selected from the group consisting of amine-terminated poly(propylene oxide), amine-terminated poly(ethylene oxide), and mixtures thereof. These polymers were said to contain sufficient amounts of ethylene oxide units to render the polymer hydrophilic. The ratio of ethylene oxide to propylene oxide groups was required to be in the range of 1.0 to 15.0.
While foams made from the polymers disclosed in U.S. Pat. Nos. 4,554,297 and 4,508,854 exhibit the levels of softness, absorbency, and resiliency desired for use in sanitary napkins and other products which absorb bodily fluids, these foams suffer from reduced mechanical strength, particularly when wet. Such loss of mechanical strength tends to compromise the structural integrity of the fluid absorbent products into which these foams are incorporated. Accordingly, there currently exists a need for hydrophilic foams which exhibit acceptable levels of wet mechanical strength.